A plurality of earth working implements, such as a gang of moldboard plow units or the like, are typically mounted on a common frame and pulled through the ground by a tractor or other suitable off-highway implement. Each plow unit is individually mounted to the frame and is designed to ensure that the plow unit maintains a desired depth in the soil as it is pulled therethrough. That is, the plow unit is designed such that, during field operations, the plow unit is prevented from "riding out" of the soil or cutting too deeply into the soil.
The resistance that is encountered by the plow units as they are pulled through the soil or ground varies considerably depending upon a number of factors. As an example, the porosity of the soil affects the resistance imparted to the tools as they are pulled through the ground. Plowing fields after a harvest was commonplace practice in years past. In view of the continued emphasis on soil conservation, however, there is a tendency to condition or plow the field less frequently than heretoforeknown. Accordingly, the soil becomes more and more compacted as off-highway equipment such as tractors and the like are driven thereover. The ability of the tool or plow unit to float or elevate in response to high resistance forces being applied thereto inhibits damage to the tool. When the field is eventually plowed, the compactness of the soil offers relatively high resistance to the tool being pulled therethrough. The presence of subterranean rocks and roots further complicates the plowing process.
U.S. Pat. No. 3,321,027 to O. E. Johnson et al discloses a unique plow mounting arrangement. The Johnson et al apparatus mounts a ground engaging tool or plow unit such that it is capable of both floating and tripping movements. That is, the Johnson et al apparatus mounts each plow unit in a manner allowing elevational movement or float of the plow unit against the action of a spring assembly when relatively high resistance or draft conditions are imparted to the implement as it is drawn through the field. The Johnson et al apparatus furthermore allows the plow units to move rearwardly and upwardly out of the ground engagement to a tripped position when abnormally high resistance or draft force is encountered by the plow unit as it is pulled through the ground. As will be appreciated, the ability of the plow unit to be tripped out of its normal operating position avoids damage to the plow unit upon engagement with a rock, root or the like. With the Johnson et al. apparatus, the plow unit is automatically returned to its operating position after the obstacle has been passed.
Today's tractors are larger than earlier versions and, thus, are capable of developing increased levels of power. The increase in power capability translates into the ability to condition the field faster than previously known. Of course, there is a direct correlation between the speed of the tractor and the resistance or draft force being applied to the plow unit being drawn thereby when the unit is in its operating position in the ground. The faster the ground speed of the tractor, the higher the draft condition being imparted to the tool.
The high resistance or draft force applied against the plow unit tends to cause the tool to elevate or float away from the depth normally obtainable with the plow unit. Increasing the spring pressure to force the plow unit downwardly does little to prevent the tool from floating. On the other hand, increasing the spring pressure likewise increases the trip load for the plow unit. As will be appreciated, increasing; the trip load endangers the plow unit in that it will not be as responsive to obstacles that would normally cause the plow unit to move to a tripped position.
Thus, there is a need and a desire for a dual action earth working implement having an earth working tool that is suspended by a linkage assembly designed to significantly increase the draft force that may be applied to the tool before the tool begins to float without significantly increasing the level of draft force that needs to be applied to the tool before the tool moves to a tripped position and without significantly increasing the spring force acting against the linkage to hold the tool in a proper working relationship during a plowing operation.